Intriguingly, the baryogenesis and dark matter problems can be solved simultaneously if M 1 ~ keV and M 2 ~ M 3 ~ GeV. ![]() The neutrino mass and mixing problem is thus solved by the usual type-I seesaw mechanism ( Minkowski, 1977 Gell-Mann et al., 1979 Yanagida, 1979 Mohapatra and Senjanovic, 1980). With the eigenstates corresponding mainly to mixings of the active left-handed neutrinos ν α, and a heavy set given by the eigenvalues M 1 < M 2 < M 3 of the matrix M, with the eigenstates corresponding to mixings of the sterile right-handed neutrinos N i. Figure 1), having Dirac masses m D = F v / 2 arising from Yukawa couplings F with the Higgs ( H) and lepton ( L i) doublets, as well as explicit Majorana masses M, Three of these problems can be tackled simultaneously in the Neutrino Minimal SM (νMSM) ( Asaka, 2005 Asaka et al., 2005): a remarkably simple extension of the SM by three right-handed singlet neutrinos N i (cf. In fact, the non-observation of an electric dipole moment of the neutron places a very strong upper limit on the angle, | θ ¯ | < 1 0 - 10, requiring an extreme fine-tuning which cannot even be justified on the basis of anthropic arguments. Last, but not least, there is the strong CP problem: the SM has no explanation for the smallness of the θ ¯-angle of quantum chromodynamics (QCD) which induces CP-violation in flavor-diagonal interactions. Furthermore, the SM does not feature masses for the active neutrinos, while the observed flavor oscillations of the active neutrinos require tiny neutrino masses. Moreover, the CP violation within the SM is too feeble to explain the asymmetry between the fraction of the baryonic matter and anti-matter in the Universe. Furthermore, the SM cannot explain the exponential expansion of the very early Universe called inflation which is required to explain the isotropic, Gaussian and nearly scale-invariant temperature fluctuations of the CMB. This evidence is supported by observations on many scales, ranging from the shapes of the rotation curves of spiral galaxies to the temperature fluctuations of the cosmic microwave background (CMB). In fact, there is compelling evidence that nearly 85% of the matter in the Universe is non-baryonic. On the other hand, it is generally agreed that there are a number of fundamental problems in particle physics and cosmology which require new physics beyond the SM. No significant deviations from the theoretical predictions of the SM have been found so far at precision collider experiments and the like. It describes the known particles and their interactions remarkably well. The SM is arguably the most successful theory in physics. Furthermore, we consider and comment on variants of SMASH. We review how this works in SMASH and discuss its further predictions and tests in astrophysics, cosmology, and laboratory experiments. The resulting extension of the SM which has been dubbed SMASH-for SM-Axion-Seesaw-Higgs portal inflation-solves the five aforementioned problems in one stroke. Furthermore, three extra SM singlet neutrinos are added who acquire their Majorana mass from the breaking of the PQ symmetry and which explain the small masses of the active neutrinos and their oscillations by the seesaw mechanism. Furthermore, the modulus of the PQ field is a candidate for driving inflation. Moreover, the pseudo Nambu-Goldstone boson of this breaking-the axion-may play the role of the dark matter. The latter may be explained by introducing an exotic vector-like quark which is charged under a chiral global U(1) Peccei-Quinn (PQ) symmetry which is spontaneously broken by the vacuum expectation value of a complex SM singlet scalar field-the PQ field. However, it lacks explanations for cosmic inflation, the matter-anti-matter asymmetry of the Universe, dark matter, neutrino oscillations, and the feebleness of CP violation in the strong interactions. The Standard Model (SM) of particle physics is a big success. 6Physik Department T70, Technische Universität München, Garching, Germany.5Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany.4Max-Planck-Institut für Physik, München, Germany. ![]() 3Departamento de Física Teórica, Universidad de Zaragoza, Zaragoza, Spain.2Departamento de Física Teórica, Universidad Autónoma de Madrid, Madrid, Spain.1Instituto de Física Teórica, UAM-CSIC, Madrid, Spain.Guillermo Ballesteros 1,2, Javier Redondo 3,4, Andreas Ringwald 5 * and Carlos Tamarit 6
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